1. Field of the Invention
The present invention relates to a switch for forwarding data transmissions between stations of a network, and in particular to a network switch having a clustered address translation system for mapping each station's network address to a switch port servicing the station.
2. Description of Related Art
Computer networks transfer data between computers or other types of network stations. For example 10BASE-T Ethernet systems use sets of twisted pair conductors in a star network topology to connect network stations to a central hub. A 10BASE-T hub is simply a repeater for receiving a data packet from any one station and concurrently rebroadcasting it to all other stations. A header in the data packet includes the network address of the intended destination station for the packet and each network station looks at the packet header to determine if it should the accept or ignore an incoming packet. Since each transmission is sent concurrently to all stations, only one network station can transmit a packet at any given time.
A network switch, unlike a network hub, forwards a data packet only to destination stations connected to a particular switch port so that not every network station receives the packet. A network switch includes a switching mechanism such as a crosspoint switch for selectively forwarding each incoming packet from an input port to an appropriate output port. The input port determines the destination output port from the network address included in the packet header and then requests a connection between the input port and the destination output port. When the connection is established, the input port sends the packet to the output port via the crosspoint switch.
Although a packet arriving at a switch port contains the network address of the station to which it is directed, the switch must relate that station's address to the station's switch port before it can forward the packet. The process of relating a network address of a destination station to the station's switch port is problematic. In a typical prior art system, as illustrated in U.S. Pat. No. 5,412,648 issued May 2, 1995 to Ruixue Fan, each input port stores an incoming packet, extracts the destination address from the packet's header and then forwards it to a central address translation unit. The central address translation unit, which maintains a look-up table relating network addresses to switch output ports, returns the output port identification (ID) to the input port. The input port then requests a connection through the switch to the indicated output port and forwards the packet to that output port. Each input port must compete with other input ports for access to the central address translation unit and as packet traffic increases so too do delays in obtaining address translations.
What is needed is a network switch in which input ports can rapidly translate network addresses into port IDs with minimal delay due to competition for central address translation services.